This invention relates generally to a poppet valve for metering the flow of fluid and more specifically to a flow amplifying poppet valve.
A poppet is a common type of low leakage, flow amplifying hydraulic control valve. A type of low leakage poppet valve is described in U.S. Pat. No. 5,137,254 and includes a cylindrical poppet valve having a poppet seat sealing against a valve seat. Fluid flow is metered between an inlet and outlet port by controllably moving the poppet valve off the valve seat.
The poppet valve includes slots to establish fluid communication between the inlet and a control chamber disposed behind the poppet valve and opposite the outlet. The fluid pressure in the control chamber exerts a closing force on the poppet valve holding it against the valve seat. A spring holds the poppet valve against the valve seat when pressure in the inlet, control chamber and outlet are equal. Adjusting fluid flow from the control chamber to the outlet varies pressure in the control chamber. A pilot valve having a variable regulating orifice controls fluid flow out of the control chamber.
The variable regulating orifice is normally closed so that fluid pressure in the control chamber equals the inlet pressure thereby urging the poppet valve against the valve seat. Opening of the pilot valve reduces pressure in the control chamber to urge the poppet valve off the valve seat when the pressure in the control chamber drops below a balance pressure. Controlling the flow through the variable regulating orifice of the pilot valve subsequently controls the degree of opening of the valve element.
A guide extension extending from the poppet seat guides along the inner diameter of the outlet. The guide extension maintains axial alignment of the poppet seat to the valve seat. The guide extension is necessary because incoming fluid flow through the inlet creates a moment force tending to tilt the poppet valve. Tilting of the poppet valve within the bore causes friction between the poppet valve and the bore inner diameter. Friction between the poppet valve and the bore inner diameter causes a great deal of unpredictability in the control of the valve.
The guide extension on the poppet seat eliminates much of the undesirable unpredictability by preventing tilting of the valve in the bore. However, as the valve opens the guide extension is pulled out of the inlet leaving progressively less of the guide extension to prevent tilting of the poppet valve. Further, in a fully open position, the guide extension is completely clear of the outlet, and provides no resistance to tilting.
An additional problem encountered in the control of a poppet valve is oscillation. Fluctuations in fluid pressure or fluid flow cause the poppet valve to oscillate. An oscillating poppet valve creates an oscillating fluid flow or fluid pressure at the outlet and is therefore undesirable.
For these reasons, a poppet valve configuration capable of reducing the effects of pressure fluctuations, and capable of preventing poppet valve tilting is needed.
The present invention is directed to overcome one or more of the problems as set forth above.
In one aspect of the invention, a flow amplifying poppet valve assembly for metering fluid flow is disclosed. The valve assembly comprises a housing defining a bore and including an inlet and an outlet presenting a valve seat. A poppet valve is slidably disposed within the bore and includes a poppet seat for engaging the valve seat to meter the flow of fluid between the inlet and the outlet. The poppet valve and housing have radially overlapping shoulders movable axially toward and away from each other to define a pressure chamber that accumulates fluid for dampening poppet valve oscillation.
The subject invention overcomes the deficiencies of prior art flow amplifying poppet valves by including a pressure chamber defined by overlapping shoulders on the poppet valve and the housing. The pressure chamber reduces the effects of pressure and fluid flow fluctuations on poppet valve position. Further, the overlapping shoulders create a constant guide length over the entire range of movement of the poppet valve thereby preventing poppet valve tilting.